1. Field of the Invention
The present invention relates to a method of controlling a semi-automatic transmission system for a motor vehicle, and a control apparatus suitable for practicing the method.
2. Discussion of the Prior Art
There is known a semi-automatic transmission system using a synchronous-mesh speed changing mechanism which is connected to an engine through an automatically controlled clutch to transmit power from the engine to drive wheels of the vehicle. In this type of semi-automatic transmission system, the automatic clutch is disengaged or released in response to an operation of an operator-controlled operating member such as a shift lever for shifting the synchronous-mesh speed changing mechanism. The operation of the operator-controlled operating member is detected by suitable means such as a switch provided on the shift lever. The speed changing mechanism is shifted to an appropriate position while the automatic clutch is in the released position. The engine is freed from a load when the automatic clutch is released. Accordingly, if the clutch is released due to an unintentional operation of the shift lever by the operator during running of the vehicle, the engine may race with its speed exceeding a critical level. To avoid this undesirable situation, suitable preventive means is provided to prevent the automatic clutch from being fully disengaged or to keep the clutch in the engaged state, despite the signal received from the activated shift lever switch, if the shift lever is operated to a gear or speed position (e.g., 1st-speed or low-gear position) in which the engine may race with its speed exceeding the critical level upon releasing of the clutch to bring the engine into a non-load state. An example of a control apparatus incorporating such preventive means is disclosed in Publication No. GB 2113341 A (published in 1983) of UK Patent Application.
In the known control apparatus of the type disclosed in the above-identified publication, for example, the automatic clutch is fully released if the shift lever is operated to a speed position (e.g., 4th-speed position) in which the engine speed will not exceed the critical level. In this case, however, the engine may more or less race with its speed rising to a considerably high level, causing racing noises and vibrations of the engine thereby deteriorating the driving comfort.